Tribological improvements of plasma immersion implanted CoCr alloys

CoCr alloys are widely used in some specific hip and knee prosthesis. In particular, they are used in advanced metal on metal (MoM) prostheses. However, while these new implants have an intermediate wear rate between low wear ceramic–metal and high wear polymer–metal prostheses, a high risk of metalosis produced by wear debris, originated in the metal–metal sliding contact, is still present. Oxygen plasma immersion ion implantation (PI3) provides a practical method to improve wear resistance of CoCr alloys, thus reducing the amount of wear particles. This paper describes the tribological and wear resistance improvements of CoCr alloy implanted by PI3. Friction and wear tests were performed to investigate the modifications obtained by oxygen implantation. Glow Discharge Optical Emission Spectrometry (GD-OES) analysis was employed to evaluate the oxide layer thickness and compositional changes of the metallic alloying elements produced by the oxygen treatment. Moreover, SEM analysis was carried out for detecting wear particles after ball on disk tests in a biological solution simulating the human body fluid.The reported results indicate that PI3 improves the wear resistance of CoCr alloy to be used in human body implants.